How to create Factory Functions instead of using Classes

Question

I am using a javascript library that is implementing ES6 class in their modules. I have not used classical inheritance in javascript and would like to essentially "undo" their class implementation. Is there a way I can take those classes and still use them in a Factory/Composition approach. I want to take advantage of JS prototypal inheritance and easy compostability of objects. The following is an example of what I have so far. Ultimately I am trying to avoid using class and new, because I am not used to using it in JavaScript. Could anyone tell me if I am approaching this in the right way or if I am just wasting my time, thank you.

class Example {

 constructor(id) {
  this.id = id;
 }

 getID() {
  console.log(this.id);
 }
}


function convertClassToObject(theClass) {
 var x = new theClass();
 var newX = Object.create(x);
 return newX;
}

var NewPrototype = convertClassToObject(Example);

function NewFactory(options) {
 var x = Object.assign(Object.create(NewPrototype), options);
 return x;
}

var NewInstance = NewFactory({id: 123456789});

class is just syntactic sugar around constructor and prototype constructs. Everything is still prototype-based underneath. new Example(id) is equivalent to var obj = Object.create(Example.prototype); obj.constructor(id). — Mike Cluck
– Mike Cluck, Commented Apr 3, 2017 at 18:43
Oh perfect, I can just link prototype with Object.create and use that instance for a factory, got it. — technoY2K
– technoY2K, Commented Apr 3, 2017 at 18:49
@MikeC Except in ES6, where constructors must be invoked with new (or super() or Reflect.construct) — Bergi
– Bergi, Commented Apr 3, 2017 at 18:53
Not sure what you mean by composition here? You can also do the object-oriented one with prototype instances, class doesn't change anything there — Bergi
– Bergi, Commented Apr 3, 2017 at 18:54

Bergi · Accepted Answer · 2017-04-03 18:50:47Z

2

You should rather get used to new, it's much simpler than doing prototypical inheritance in factories.

Of course, it's trivial to convert a constructor function to a factory function:

function classToFactory(constr) {
    return (...args) => new constr(...args);
}

const makeExample = classToFactory(Example);
const newInstance = makeExample(123456789); // no `new` any more

answered Apr 3, 2017 at 18:50

Bergi

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1 Comment

technoY2K Over a year ago

I guess I could try getting used to the new keyword. Thank you for your insight.

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